1. Field of the Invention
This invention relates to improvements in a combustion control system for a diesel engine, and more particularly to the combustion control system for effecting a low temperature premix combustion in a combustion chamber of the engine so as to improve exhaust emission performance and combustion noise performance of the engine.
2. Description of the Prior Art
Hitherto a variety of techniques for improving exhaust gas performance and combustion noise performance of a diesel engine has been proposed and put into practical use. One of them is disclosed in Japanese Patent Provisional Publication No. 8-86251 and configured as follows: A fuel injection timing is retarded to a timing after top dead center on compression stroke thereby prolonging a so-called ignition delay period of between a fuel injection initiation timing and an ignition timing of injected fuel. During this prolonged ignition delay period, a pre-mixture of air and fuel is formed in the combustion chamber by lowering an oxygen concentration owing to exhaust gas recirculation and by controlling gas flow in the combustion chamber, thus accomplishing a so-called low temperature premix combustion.